Process of plating metal



Patented July 21, 1931 UNITED STATES PATENT OFFICE WILLIAM E. WATKINS, OF NEW YORK, N. Y., ASSIGNOR TO COPPER PLATE SHEET & TUBE COMPANY, OF NEW YOR K, N. Y., A CORPORATION OF NEW JERSEY PROCESS OF PLATING METAL No Drawing.

This invention relates to the plating of metal articles, such as sheets or strips of 1ron or steel, and more particularly to a method of forming a plating suspension of two or 5 more metals on a sheet or strip of metal, then heating the coated metal to cause one of the coating metals to diffuse into the other and then heating the coated metal to a higher temperature to form an adherent, non-strip- 1 ping film of an alloy of the two plating metals on the sheet or strip. 7

This invention may be understood by considering its application to the plating or iron or steel sheets. In the production of a nonferrous covering on. a ferrous base, the present universal practice is to take the iron or steel sheets from the hot rolls of the rolling mill, and stack them in piles in a Mesta pickler crate operated by a plunger which moves the crate up and down in an acid solution until all of the iron oxide on the sheets has been removed. The crate containing the sheets or plates is then transferred to a bath of water where it is plunged upand down until the sheets have been thoroughly cleaned. The sheets are then stacked in piles on an iron car and covered with an inverted iron pot, the interstices between the iron pot and the floor of the car being chinked with sand to prevent admission of air. The car with its piles of sheets is then pushed into what is commonly known as a box annealing oven, which is heated from 1400 to 1800 F. at the roof and left there until the temperature of the sheets, if full finished stock, has been raised to approximately 1150 F. This annealing requires from 15 to 20 hours, depending upon the gauge of the sheets. The heat is then turned off and the room with its contents allowed to cool sufficiently to permit the removal of the car containing the sheets. After removal from the annealing oven the sheets are cooled to a temperature at which they will not oxidize when the inverted pot cover is removed,

Application filed May 24,

be plated, the sheets are cold rolled for the 1929. Serial No. 365,785.

purpose of giving them a fine-grained surface. This rolling makes the sheets too hard to be fabricated, and they must again be annealed and pickled before they can be plated, after which they are usually passed into a receptacle known as a water bosh, containing water, in order to exclude the air from the surfaces of the sheets until they are taken out and passed through a bath of molten non-ferrous metal. ,These latter operations are know as white annealing and white pickling.

The above described process, now in universal use, is both ineflicient and wasteful. For instance, in the black and white pickling operations reliance is placed on the repeated plunging of the pickler crate to separate the sheets sufficiently to permit the acid to re= move all of the oxide. In order to secure satisfactory results, the black pickling should be continued for approximately 4 minutes and the white pickling for approximately 2 minutes. This prolonged exposure of the sheets to the action of the acid results in excessive loss of the ferrous metal. I have found, in actual commercial practice, that by using my improved method, it is not necessary to expose the ferrous metal to the action of the acid for more than one minute, and the loss of ferrous metal is less than'one-half of the loss occurring when present, methods are employed. I

The annealing of the sheets in stacks or piles is not conducive to the production of a uniform product having the desired fabrithe surfaces of the plates would become soft enough to cause the sheets to stick together. The present invention makes it possible to subject each sheet to the proper annealing temperature, and being done singly the sheets cannot stick together.

According to the present invention, the sheets are given a preliminary treatment for the purpose of straightening them, for removing any oxides present on the surfaces thereof, and for imparting to the sheets the desired surface characteristics. The sheets are then covered with a plating mixture containing two or more metals in finely divided form, and capable of forming an alloy which is to become the plating layer on the ferrous sheets. In general, the method of applying the coatinglayer consists in covering the sheets with finely divided plating material, such as finely divided copper and finely divided zinc carried by a suitable liquid, which provides a proper distribution of the finely divided metal upon the plates, and maintains this distribution until the finely divided material, when subjected to heat, forms a non-stripping union with the plates. The coated metal is then submitted to a heat treatment below the volatilization point of zinc for the purpose of causing it to diffuse into the copper and form a brass coating on the base metal. The coated metal is then submitted to a higher temperature to form,

an adherent, non-stripping layer or plating.

of the alloy on the base metal.

In my copending application Serial No. 358,438, filed April 26, 1929, I have disclosed and claimed the process of plating a metal with an alloy in which a layer of one constituent of the alloy is firstapplied to the base metal, a layer of the second constituent of the alloy then applied and the'plated metal heated to form a coating or plating of the alloy of said plating metals. In practicing the present invention the ferrous metal, or other base, is first coated with a plating suspension containing the two or more metals to be alloyed, in finely divided form. Thus finely divided copper particles, and finely divided zinc particles, in proper proportion to form finely divided brass particles, are suspended in a suitable liquid spreading medium, such as an asphaltic base hydrocarbon oil, and a film of the mixtureapplied to the ferrous strips or sheets to be plated. This mixturemay be applied in any suitable manner, as by spraying or brushing, but I prefer to use thecoating apparatus disclosed in my prior Patent No. 1,295,820.

The sheets or strips, coated with the mixture, are then heated to a temperature below the volatilizing temperature of the zinc, to cause the zinc particles to difiuse into the copper particles and form brass particles. A temperature of 500 to 550 C. may be employed for this purpose. The coated metal is then heated to a temperature that will produce, from the brass particles, in the coating, a non-stripping plating of brass on the metal to be plated. A temperature of 900 to 1200 C. may be employed for this purpose.

The heating treatmentsmay be carried out in the furnace described and claimed in my prior Patent No. 1,679,889. The apparatus therein described comprises a preliminary heating zone and a main heating zone. This construction admits a low temperature to be carried in the preliminary heating zone, and a high temperature in the main heating zone. The length of the preliminary heating zone may be proportioned to the contemplated speed of travel of the material to obtain the desired heat treatments in each part of the furnace. Under such conditions a sheet or strip coated in the manner described above, and passed through the heating apparatus will emerge therefrom with a strongly adhering, non-stripping plating of brass thereon. The brass, being formed before the coated metal is passed into the main heating zone and submitted to a plating temperature of from 900 to 1200 C., will not be unfavorably affected by such temperatures.

According to the present invention, thehot rolled sheets are passed, one at a time, between rolls which straigthen them and deliver them to a conveyor which travels through a shallow tank containing dilute acid. The sheets are subjected to the action of the acid for a time and at a temperature sufficient to remove the oxides on the surfaces of the plates. From the acid bath conveyor, the sheets are conveyed through a water spray which washes the sheets thoroughly. After the sheets have been cleaned in this manner, they are passed between heated drying rolls. The sheets are then covered with the plating mixture which ultimately becomes the plating layer on the iron sheets. If it is so desired, the sheets may be passed between heavy surfacing rolls before the sheets are covered with the coating mixture, the object being to give the sheets a line grained, smooth surface.

The first step of the plating process proper, consists in applying to the article to be plated, a coating of finely divided plating material, preferably copper, and zinc out of which a permanently adhering or non-stripping plating can be formed. If the articles are in the form of sheets, say of iron or steel, this coating may be applied by means of rotatingl rolls between which the sheets ar passed. A coating machine which may be ememma ployed to advantage for this purpose is shown in my Patent No. 1,295,820. In general, this coating machine includes a mixing tank and a pair of coating rolls between which fiat sheets may be passed to receive the viscous composition containing the finely divided metal in suspension. The mixing tank contains an agitator for maintaining the proper homogeneity of the composition, and means is provided for pumping the agitated composition from the tank and spreading it on each of the coating rolls in a substantially uniform layer.

The sheets to which the plating mixture has been applied are then passed into the preliminary heating zone and heated to a temperature of from 500 to 550 C. The temperature is thus maintained below the volatilization point of the zinc until the zinc is diffused into the copper. The preliminary heating chamber may be made of a proper length to permit this preheating of the coated sheet without interfering with the operating speed through the main plating chamber. The sheets, after the preliminary heating, are passed into the main plating chamber which is maintained at a temperature of from 900 to 1200 C. at which temperature a non-stripping, adhering plating of brass will be formed on the base metal. The preliminary heating causes the zinc to diffuse into the copper and form brass and the brass having been formed before the metal is submitted to the plating temperature is not unfavorably affected at such temperatures.

The process may be also applied to the formation of a bronze coating on a sheet or strip in which case, the plating mixture is formed of finely divided particles of copper and tin, and a liquid spreading medium. The coated metal is passed through the preheating chamber which is maintained at a tern perature of substantially 300 C. and then through the main plating chamber in the manner heretofore described.

The vehicle employed for the purpose of spreading the finely divided material uniformly over the sheets mavbe any suitable liquid, preferably of a reducing character.

Oil, having an asphaltic base, is particularly suitable; and I have found'that Mexican or Oklahoma crude petroleum having a specific gravity corresponding to 7 to 7 lbs. to the gallon gives very satisfactory results. This crude oil possesses the desired spreading properties and the ability to hold the finely divided material in suspension; and its viscosity, reducing characteristics and cheapness render it particularly valuable for this purpose. In the event that a non-reducing vehicle is employed, I prefer to incorporate a reducing agent, such as finely divided carbon, the reducing agent being thoroughly mixed with the liquid and the plating material. Even when a reducing vehicle is employed,

it is oftentimes desirable to add a small quantity of a reducing agent to supplement the reducing action of the vehicle. A mixture hav ing the proportions of 1 oz. of carbon to one pound of finely divided plating mixture and one pound of Mexican petroleum gives desirable results.

I claim:

1. The method of forming a plating of an alloy of two or more metals on a metal base which comprises forming a liquid plating mixture containing the metals of the alloy in finely divided form, applying the plating mixture to the metal base, subjecting the coated metal to a temperature that will cause one of the plating metals to diffuse into the other to form the desired alloy, said temperature being less than the melting temperature of either of said metals, maintaining the temperature of the sheet below the melting temperature of the coating metals until an alloy of the coating metals is formed and then subjectin'g the coated metal to a temperature sufficient to form a non-stripping plating of the alloy on the metal base.

2. The method of forming'a plating of an alloy of two or more metals on a metal base comprising forming a liquid plating layer containing the metals of the alloy in finely divided form on the metal base, subjecting the coated metal to a temperature that will cause one of the plating metals to diffuse into the other plating metal to form the desired alloy, said temperature being less than the melting temperature of either of said metals, maintaining the temperature of the sheet below the melting temperature of the coating metals until an alloy of the coating metals is formed and then subjecting the coated metal to a temperature sutficient to form a non-stripping plating of the alloy on the metal base.

3. The method of making brass plating on a ferrous base which consists in forming a liquid plating mixture containing finely divided copper and finely divided zinc, applying the plating mixture to the ferrous base, subjecting the ferrous base coated with the plating mixture to a temperature which will form brass by diffusion of the zinc into the copper of the mixture, said temperature being less than the melting temperature of zlnc, maintaining the temperature of the sheet below the melting temperature of zinc until an alloy of copper and zinc'is formed and then subjecting the coated ferrous base to a temperature sufficient to form a nonstripping plating of brass on the ferrous base.

4. The method of making brass plating on a ferrousbase which consists in forming a plating mixture containing finely divided copper and finely divided zinc, applying the plating mixture to the ferrous base, subjecting the ferrous base coated with the plating mixture to a temperature of 500 to 550 C.

Ill)

to cause the zinc to diffuse into the copper of the mixture to form brass, said temperature being less than the melting temperature of zinc, maintaining the temperature of the sheet below the melting temperature of zinc until an alloy of copper and zinc is formed and then subjecting the brass coated ferrous base to a temperature of 900 to 1200 C. to form a non-stripping plating of brass on the ferrous base.

In testimony whereof I affix my signature.

WILLIAM E. WATKINS. 

